Close
About
FAQ
Home
Collections
Login
USC Login
Register
0
Selected
Invert selection
Deselect all
Deselect all
Click here to refresh results
Click here to refresh results
USC
/
Digital Library
/
University of Southern California Dissertations and Theses
/
Effects of bilateral stimulation and stimulus redundancy on performance in processing nonword letter trigrams
(USC Thesis Other)
Effects of bilateral stimulation and stimulus redundancy on performance in processing nonword letter trigrams
PDF
Download
Share
Open document
Flip pages
Contact Us
Contact Us
Copy asset link
Request this asset
Transcript (if available)
Content
INFORM ATION TO USERS This manuscript has been reproduced from the microfilm master. UMI films the text directly from the original or copy submitted. Thus, some thesis and dissertation copies are in typewriter free, while others may be from any type of computer printer. The quality of this reproduction is dependent upon the quality of the copy submitted. Broken or indistinct print, colored or poor quality illustrations and photographs, print bleedthrough, substandard margins, and improper alignment can adversely affect reproduction. In the unlikely event that the author did not send UMI a complete manuscript and there are missing pages, these will be noted. Also, if unauthorized copyright material had to be removed, a note will indicate the deletion. Oversize materials (e.g., maps, drawings, charts) are reproduced by sectioning the original, beginning at the upper left-hand corner and continuing from left to right in equal sections with small overlaps. Each original is also photographed in one exposure and is included in reduced form at the back of the book. Photographs included in the original manuscript have been reproduced xerographically in this copy. Higher quality 6” x 9” black and white photographic prints are available for any photographs or illustrations appearing in this copy for an additional charge. Contact UMI directly to order. UMI A Bell & Howell Information Company 300 North Zeeb Road, Ann Arbor MI 48106-1346 USA 313/761-4700 800/521-0600 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. EFFECTS OF BILATERAL STIMULATION AND STIMULUS REDUNDANCY ON PERFORMANCE IN PROCESSING NONWORD LETTER TRIGRAMS by Nancy Lee Marks A Thesis Presented to the FACULTY OF THE GRADUATE SCHOOL UNIVERSITY OF SOUTHERN CALIFORNIA In Partial Fulfillment of the Requirements for the Degree MASTER OF ARTS (Psychology) August 1998 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. UMI Number: 1393178 UMI Microform 1393178 Copyright 1999, by UMI Company. All rights reserved. This microform edition is protected against unauthorized copying under Title 17, United States Code. UMI 300 North Zeeb Road Ann Arbor, MI 48103 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. U N IV E R SITY O F S O U T H E R N C A L IF O R N IA T H E GRADUATE SC H O O L UNIVERSITY PARK LO S A N G ELES. C A LIFO RN IA S0007 This thesis, written by ___________ Nancy Lee Marks______________ under the direction of h&£. Thesis Committee, and approved by all its members, has been pre sented to and accepted by the Dean of The Graduate School, in partial fulfillment of the requirements for the degree of Master o f Arts rtnt* J u n e 1 6 > 1 9 9 8 THESIS COMMI Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Table of Contents Section Page List of Figures.......................................................................................................... iii Abstract .................................................................................................................... iv Introduction................................................................................................................ 1 Experiment 1 ............................................................................................................. 6 M ethod.......................................................................................................... 8 Results and Discussion................................................................................. 11 Experiment 2 ............................................................................................................. 17 M ethod.......................................................................................................... 18 Results and Discussion.................................................................................21 General Discussion................................................................................................... 24 References .................................................................................................................30 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. iii List of Figures Figure 1. Illustrations of the same CVC target presented in three different viewing conditions in Experiment 1........................................................9 Figure 2. Percentage of errors for each of the three visual field conditions in Experiment 1. Error bars show standard errors computed from the within-subject error term (Loftus & Masson, 1994). (FE = normalized first-letter errors; LE = normalized last- letter errors; OE = normalized other errors.).......................................................14 Figure 3. Illustrations of the same CVC targets presented in different viewing conditions in Experiment 2................................................. 20 Figure 4. Percentage of errors for each of the three visual field conditions in Experiment 2. Error bars show standard errors computed from the within-subject error term (Loftus & Masson, 1994). (FE = normalized first-letter errors; LE = normalized last- letter errors; OE = normalized other errors.)...................................................... 23 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Abstract Performance in a nonword letter trigram identification task was investigated in two experiments in which the number of physical stimuli and number of targets were controlled. In Experiment 1 the target consonant-vowel-consonant (CVC) trigram was projected on each trial to the left hemisphere (RVF/left hemisphere), right hemisphere (LVF/right hemisphere), or both hemispheres simultaneously (BILATERAL). In both target-unilateral conditions, a noise stimulus was projected to the visual field contralateral to the target, thus insuring bihemispheric stimulation on all trials. Quantitative performance on BILATERAL trials showed the redundancy gain predicted by the binomial theorem, indicating that the two cerebral hemispheres share a common pool of processing resources. Qualitative performance was more similar to right hemisphere than left hemisphere performance. In Experiment 2, two copies of the target CVC were projected on every trial along with two copies of the noise stimulus. Performance was optimal when both target CVCs were projected directly to the left hemisphere (RVF/left hemisphere). When one target CVC was projected to each hemisphere (BILATERAL) trials, quantitative performance exceeded the average of the unilateral conditions, which may indicate that each hemisphere has available some separate processing resources, unshared by the other hemisphere, which can be tapped when input is bihemispheric. On BILATERAL trials, qualitative performance was again more similar to right hemisphere than left hemisphere performance. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 1 Effects of Bilateral Stimulation and Stimulus Redundancy on Performance in Processing Nonword Letter Trigrams The important issue of how the two cerebral hemispheres work together to produce a unified response can be studied in neurologically intact individuals using tasks for which both hemispheres have some competence, but for which they differ in their preferred mode of processing (Hellige, 1987; Hellige, Jonsson, & Michimata, 1988). Hellige and his colleagues (Hellige, Taylor, & Eng, 1989) have noted that the lateralized nonword letter trigram identification task is one such task in which qualitative differences in performance arise when stimuli are presented to the right visual field/left hemisphere (RVF/left hemisphere) or the left visual field/right hemisphere (LVF/right hemisphere). By comparing performance on bilateral redundant trials (BILATERAL), in which the same stimulus information is available to both hemispheres, with performance on unilateral trials, these researchers and others (e.g., Cherry, Hellige, & McDowd, 1995; Eng & Hellige, 1994; Hellige et al., 1994; Luh & Levy, 1995) have made inferences about interhemispheric interaction and cooperation. In the lateralized nonword letter trigram identification task, observers are asked to identify consonant-vowel-consonant (CVC) trigrams flashed briefly to the left or right visual field or to both visual fields simultaneously. For most right-handed observers, performance is much better for syllables presented to the right visual field (RVF) and thus processed initially by the left hemisphere than for syllables presented to the left visual field (LVF) and thus processed initially by the right hemisphere. This left hemisphere advantage is consistent with the reputed superiority of that hemisphere for processing of verbal information. Therefore, one might expect to find that for BILATERAL presentations, in which both hemispheres have access to identical stimulus information, the mode of processing favored by the more verbal left Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 2 hemisphere would tend to dominate. On this view, performance on BILATERAL trials would be qualitatively very similar to performance on RVF/left hemisphere trials (or at least more similar to it than to performance on LVF/right hemisphere trials). However, qualitative analyses of performance on BILATERAL trials in CVC identification experiments conducted by Hellige and his colleagues and others have found that the pattern of performance on BILATERAL trials is either statistically equivalent to that on LVF/right hemisphere trials or more similar to it than to performance on RVF/left hemisphere trials (Cherry et al., 1995; Hellige & Cowin, 1996; Hellige et al., 1989; Luh & Levy, 1995). For the purpose of qualitative analysis in this and previous studies, errors have been classified using a classification system suggested by Levy, Heller, Banich, and Burton (1983; see also Levy & Reid, 1978). Trials on which the first letter was missed but the last letter was correct are classified as first-letter errors (FEs); trials on which the last letter was missed but the first letter was correct are classified as last-letter errors (LEs); and all other errors are classified as other errors (OEs). For FEs and LEs, correctness of the vowel is irrelevant. Scores are normalized for each visual field by dividing the FE, LE, and OE scores by the total number of errors (FE + LE + OE) for that visual field. For all visual field conditions, there are more LEs than FEs, but this difference is proportionately greater for the LVF/right hemisphere than for the RVF/left hemisphere, indicating a proportionately greater tendency to miss the last letter of the trigram. This result has been interpreted as suggesting that the left hemisphere uses a more holistic processing strategy, distributing attention more rapidly and equally over the trigram, while the right hemisphere uses a more serial, letter-by-letter approach (Eng & Hellige, 1994; Hellige & Cowin, 1996; Hellige, Cowin, & Eng, 1995; Levy et al., 1983; Luh & Levy, 1995). To focus attention on Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 3 the proportion of LEs to FEs, Levy et al. calculated a qualitative error (QE) score by subtracting the normalized percentage of FEs from the normalized percentage of LEs. The greater the preponderance of LEs over FEs, the higher the QE score will be. The conclusion that performance on BILATERAL trials is more similar to performance on LVF/right hemisphere trials than to performance on RVF/left hemisphere trials has been based on a comparison of QE scores in the three visual field conditions and on an analysis of the interaction of visual field with error type (e.g., Hellige et al., 1989; Luh & Levy, 1995). The existence of this interaction defines a qualitative difference in performance across visual fields (Hellige, 1983). Although qualitative performance on BILATERAL trials appears similar to that on LVF/right hemisphere trials, quantitative performance has usually been found to be about the same as performance on RVF/left hemisphere trials or only slightly better. When a central digit identification has been required to insure fixation, BILATERAL quantitative performance has not exceeded RVF/left hemisphere performance. For example, Hellige et al., 1989, Experiment 1, reported error rates of 61.3%, 38.8%, and 38.6% for the LVF, RVF, and BILATERAL trials respectively; and Luh and Levy, 1995, reported error rates of 62.5%, 42.7%, and 45.1% for the LVF, RVF, and BILATERAL trials respectively. When no fixation digit has been used (and only a small plus sign has served as a fixation mark), BILATERAL performance has been statistically equivalent to or only somewhat better than RVF/left hemisphere performance. For example, Hellige et al., 1989, Experiment 2, reported error rates of 61.3%, 42.9%, and 38.8% for the LVF, RVF, and BILATERAL trials respectively; Eng and Hellige, 1994, Experiment 2 (CVCs) reported error rates of 61.5%, 47.4%, and 37.7% for the LVF, RVF, and BILATERAL trials respectively; and Hellige and Cowin, 1996, Experiment 2, reported error rates of 61.4%, 47.2%, and 38.7% for the Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 4 LVF, RVF, and BILATERAL trials respectively. These results are apparently inconsistent with a model of bihemispheric cooperation in performance of the task, in which a correct answer by either hemisphere would lead to a correct response (statistical summation or the binomial theorem). The binomial formula predicts accuracy if the two hemispheres are processing the bilaterally presented stimuli independently, each able to achieve the same level of accuracy as it can on unilateral trials, and then combining the results of their calculations. According to the binomial theorem, the probability of a correct response on BILATERAL trials, P(BVF), should be equal to P(RVF) + P(LVF) - P(RVF)*P(LVF). Since experimental results for BILATERAL trials have been much lower than this prediction, Hellige and his colleagues have suggested that performance on BILATERAL trials may be limited by constraints on the mode of bihemispheric processing, with both hemispheres using a relatively more sequential strategy when they must work together to process identical stimulus information (Hellige et al., 1989). These researchers showed that for their data a model in which both hemispheres used the sequential mode of processing of the right hemisphere was consistent with quantitative performance on BILATERAL trials. More recently, Luh and Levy (1995) have advanced the hypothesis that the relatively low level of bilateral performance compared to the prediction of the binomial theorem represents a balance between the advantage of having two processing units (the two cerebral hemispheres) and the attentional costs of bilateral stimulation. Bilateral displays may be non-redundant (different stimulus information is presented to each hemisphere) or redundant (the same stimulus information is presented to each hemisphere). Under some conditions, notably when tasks are more demanding, displays in which non-redundant stimuli are divided across the two visual fields have been found to produce better performance than unilateral displays, presumably because Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 5 of some advantage of interhemispheric cooperation (Banich & Belger, 1990; Belger & Banich, 1992; Liederman, Merola, & Martinez, 1985; Ludwig, Jeeves, Norman, & DeWitt, 1993; Merola & Liederman, 1990; Norman, Jeeves, Milne, & Ludwig, 1992). For example, when subjects are asked to compare two simultaneously presented letters, one upper case and one lower case, performance is better when one is presented in each visual field rather than both letters being presented in the same visual field. This phenomenon is termed the bilateral advantage. However, researchers have also noted performance degradation under some conditions when non-redundant stimuli are presented bilaterally rather than unilaterally (e.g., Banich & Karol, 1992; Boles, 1983; Bryden & Bulman-Fleming, 1994; Butler & Bryden, 1990; Duncan, 1980; Hines, 1975; Liederman, 1986; McKeever, 1971; McKeever & Huling, 1971; Young & Bion, 1981). For example, in the letter comparison task, when the two characters to be compared are in the same case and font, performance is better when they are both presented in the same visual field. In addition, when competing stimuli are presented in the two visual fields, any performance asymmetry tends to be magnified, perhaps because of a disruption of callosal transfer when homologous areas of the two hemispheres are simultaneously activated (Boles, 1990,1995). In the case of bilateral redundant displays, performance advantages could accrue from redundancy gain (when unilateral displays have only one copy of the target) as well as from interhemispheric cooperation. For example, bilateral redundant displays have been found to produce somewhat better performance for word recognition than unilateral displays, although not as much as would be predicted under conditions of statistical summation (e.g., Jones, 1982). Under some conditions, bilateral redundant displays have even been found to produce some costs relative to unilateral displays (e.g., Banich & Karol, 1992). Hellige, Jonsson, and Michimata Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. (1988) reported performance degradation for bilateral redundant stimulation compared to unilateral stimulation in a face comparison task. They suggested that any processing resources common to the two hemispheres must be divided between the hemispheres when people are presented with demanding bilateral stimulation. In the case of bilateral redundant displays, performance degradation could result from distraction effects (Grice, Canham, & Gwynne, 1984) or from some costs of interhemispheric transfer. Whether bihemispheric stimulation produces performance advantages or decrements evidently depends on both the stimuli and the nature of processing required for a task. In the case of the CVC identification task, one would expect to find a redundancy gain from having two targets in bilateral displays and perhaps some performance advantage due to dividing the initial perceptual input between the two hemispheres. On the other hand, one might expect also to find some performance decrement due to doubling of the perceptual load or distraction and perhaps to some costs related to interhemispheric transfer of information. Experiment 1 The implicit assumption underlying inferences about hemispheric interaction or cooperation from performance on bilateral redundant trials in the standard CVC paradigm, as Jerre Levy has pointed out (personal communication with Joseph B. Hellige, February 21, 1996), may be that each hemisphere has available to it the same processing resources and is able to achieve the same level of performance on bilateral redundant trials as on unilateral trials. However, this assumption is certainly questionable. In the usual CVC paradigm, only one stimulus is presented on unilateral trials, and it is presented to only one visual field, so only one hemisphere is stimulated. On bilateral trials, however, two stimuli are presented, one to each visual field, so both hemispheres are stimulated. To the extent that the two hemispheres share Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 7 some common processing resources, each hemisphere will have fewer resources to devote to processing the stimulus on bilateral trials than it would have on unilateral trials. Experiment 1 was designed to control for this potential confound by equating the number of physical stimuli and the number of hemispheres stimulated on each trial. Two stimuli were presented on all trials, one in each visual field. For those trials in which the target was presented to either the LVF/right hemisphere or the RVF/left hemisphere, the contralateral visual field was occupied by a noise stimulus (a series of three Xs). In all other respects, Experiment 1 was similar to earlier CVC experiments performed by Hellige and colleagues (cf. Hellige et al., 1989, Experiment 2). It was assumed that the presence of an irrelevant but similar stimulus (a letter trigram in the same font as the CVC) would require processing resources from the hemisphere contralateral to the one processing the CVC, thus producing a division of resources similar to that occurring on BILATERAL trials. The remaining significant difference between RVF/left hemisphere trials and LVF/right hemisphere trials, on the one hand, and BILATERAL trials, on the other hand, would be that two copies of the target would be available for processing, one by each hemisphere, on BILATERAL trials. With the amount of available attentional resources equated across visual field conditions, it was expected that the BILATERAL condition would show an increased redundancy gain as compared to the target- unilateral conditions. No longer offset by a comparative reduction in attentional resources, as it has been in the standard CVC paradigm, the advantage of having two copies of the target CVC available for processing and of having both hemispheres contributing to processing would be revealed. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 8 Method Participants. Ten men and 10 women university students participated in Experiment 1. Participants received extra credit in psychology courses. All were right- handed native speakers of English and had normal or corrected-to-normal vision in both eyes by self report. Participants ranged in age from 17 to 22 years (M =18.9 , S.D. = 1.33). Preliminary analyses indicated no effects involving gender, so the results presented in this paper are collapsed across men and women. Apparatus and stimulus materials. All stimuli were prepared and presented on a Macintosh Ilci computer with a 13-inch AppleColor High Resolution RGB Monitor (M l297) using the MacProbe software package from Aristometrics, Inc. Stimuli consisted of 37 consonant-vowel-consonant (CVC) nonword trigrams formed from the consonants D, F, G, K, P, S, and T and the vowels A, E, and O. In addition, a trigram consisting of three X's was used as a noise stimulus (the foil). An additional 12 different CVCs were used for a block of 36 practice trials. The trigrams were in Helvetica Black 24 pt. font, oriented vertically, and displayed in white against a dark blue background on the computer monitor. Each trigram subtended 0.5 ° of visual angle horizontally and 3.2° of visual angle vertically when viewed at a distance of approximately 57 cm from the screen. Participants used a chin rest as well as a forehead bar to limit head movement and maintain viewing distance. The stimuli were presented in two positions on the screen: LVF, centered 3° left of fixation, and RVF, centered 3° right of fixation. In the LVF condition, the CVC was presented to the left of fixation and a trigram consisting of three X's (the foil) was presented to the right; in the RVF condition, the CVC was presented to the right of fixation and the foil was presented to the left; in the BILATERAL condition, the CVC was presented in both visual fields. In all three conditions, each side of the screen Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 9 contained either a CVC or a foil. Illustrations of these three viewing conditions are given in Figure 1. Unilateral LVF/RH Unilateral RVF/ LH Bi lateral Figure 1. Illustrations of the same CVC target presented in three different viewing conditions in Experiment 1. Trials were arranged in three blocks of 37 trials each. The first trial in each block served only to define the “previous trial type” for the second trial in the block, and thus the first trial in each block was not scored. Each CVC appeared once in the LVF, once in the RVF, and once in both visual fields simultaneously (BILATERAL). However, each CVC appeared only once in each block, with 12 of the scored CVCs in a given block appearing in each of the three visual field conditions. Within each block the CVCs were arranged pseudo-randomly, with the limitation that each visual field Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 10 condition followed each of the others equally often and no more than four consecutive trials were in any given visual field condition. A pattern mask was displayed in each screen position following the offset of the stimuli. The masks were composed of thin black and white horizontal bars. Each mask subtended approximately 3° of visual angle horizontally and 4° of visual angle vertically and was centered 3° to the right or left of fixation. Procedure. Participants filled out a handedness questionnaire based on Oldfield’ s adaptation of the Edinburgh Handedness Inventory (Oldfield, 1971) and were judged to be right handed if they wrote and drew with their right hands and did not report any pressure to use their right hand rather than their left hand in childhood. Participants were told that on each trial a CVC would be presented in the left visual field (with a string of three Xs in the right visual field); in the right visual field (with a string of three Xs in the left visual field); or in both visual fields simultaneously, in which case the two copies of the CVC would always be the same. They were instructed to ignore the Xs, since the CVC would never contain an X. Trials began with a 2 s display of a small white fixation cross in the center of the computer screen, followed by the presentation of the trigrams. Immediately at the offset of the trigrams, the pattern mask appeared in both visual fields for 210 ms. Participants were instructed to maintain fixation on the fixation cross for the duration of the trial and to report the CVC by first pronouncing it and then spelling it, guessing when they were unsure. The experimenter entered their responses in the computer, and the next trial was immediately initiated. To insure an error rate near 50% for qualitative analysis, exposure duration of the CVCs was titrated as follows: on the first practice trial, the exposure duration was set at 195 ms. Thereafter, each correct response shortened the duration of the next trial by 15 ms, and each incorrect response lengthened the duration Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 11 of the next trial by 15 ms. The maximum exposure duration was set at 210 ms in order to avoid eye movements. The exposure duration for the final practice trial was used for the first experimental trial, and the titration procedure continued throughout the experiment Results and Discussion The titration of exposure durations resulted in approximately equal durations for all three visual field conditions (LVF/right hemisphere M = 47 ms; RVF/left hemisphere M = 48 ms; BILATERAL M = 49 ms). These exposure durations successfully yielded an overall CVC identification error rate near 50% (specifically, 44.4%, S.D. = 7.3%). However, the error rates for the three visual field conditions differed significantly, F(2,38)=35.89, MSE = .0182, pc.001. Subsequent post hoc comparisons showed that all three visual field conditions differed from each other significantly in error rate (p < .001 in all cases). The error rate for the LVF/right hemisphere (62.9%, S.D. = 16.2%) was larger than that for the RVF/left hemisphere (42.9%, S.D. = 14.0%), showing the expected RVF/left hemisphere over LVF/right hemisphere advantage. This left hemisphere advantage of 20% is somewhat greater than that reported in earlier CVC experiments, when the visual field opposite that containing the CVC was empty and no fixation digit was used (e.g., Hellige & Cowin, 1996, Exp. 2, 14.2%; Hellige et al., 1989, Exp. 2, 17.3%; Levy et al., 1983, 15%). An increased magnitude of asymmetry is generally found when bilateral displays containing two competing stimuli are compared to unilateral displays (Boles, 1983, 1990, 1995; McKeever, 1971). The 20% asymmetry found in the present experiment is comparable to that found in previous experiments using a fixation digit (e.g., Hellige et al., 1989, Exp. 1, 22.5%; Luh and Levy, 1995, 19.8%). Note that increased magnitude of asymmetry with the addition of a central fixation digit to a Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 12 unilateral display has been found by Boles (1983), who argued that the central fixation digit, by crossing the midline, creates a bilateral display. The error rate for BILATERAL trials was 26.8% (S.D. = 8.1%), which is much lower than the error rate for either LVF/right hemisphere or RVF/left hemisphere. In fact, accuracy for BILATERAL trials, at 73.19%, was not significantly different from the accuracy predicted by the binomial formula, P(RVF) + P(LVF) - P(RVF)*P(L VF), of 73.63%, t(19) =.1867, p = .85. Recall that the binomial formula predicts accuracy if the two hemispheres are processing the bilaterally presented stimuli independently, each able to achieve the same level of accuracy as it can on unilateral trials, and then combining the results of their calculations. The high level of performance on BILATERAL trials relative to LVF/right hemisphere and RVF/left hemisphere trials is in contrast with results of earlier CVC experiments in which unilateral trials involved only a single stimulus, that is, the field opposite the CVC was blank. In most of these earlier experiments, the error rate for bilateral redundant presentations was only somewhat lower than the error rate for RVF/left hemisphere presentations, but not as low as would be predicted by the binomial formula, or was even slighdy higher than the error rate for RVF/left hemisphere presentations (when fixation digits were used). The superior performance obtained on BILATERAL trials compared to target-unilateral trials in the present experiment supports the experimental hypothesis that the expected redundancy gain from having two copies of the stimulus available would emerge once the number of stimuli and hemispheres stimulated on each trial was controlled. On trials where the target was presented unilaterally, the foil (three letter Xs) was an irrelevant noise stimulus, competing for attention without contributing to performance. However, on trials where the target was presented bilaterally, the two stimuli were redundant copies, so both Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 13 were informative and could contribute to a correct response. Whatever attentional costs were incurred due to bilateral stimulation were equated for all visual field conditions. The level of performance observed is consistent with the hypothesis that on BILATERAL trials, both hemispheres actively process the CVC and contribute to observed performance. To examine performance in the three visual field conditions more closely, errors were analyzed according to the classification previously used by Hellige et al. (e.g., 1989, 1995, 1996) and by Levy et al. (1983). Recall that trials on which the first letter was missed but the last letter was correct were classified as first-letter errors (FEs); trials on which the last letter was missed but the first letter was correct were classified as last-letter errors (LEs); and all other errors were classified as other errors (OEs). For FEs and LEs, correctness of the vowel was irrelevant. Scores were normalized for each visual field by dividing the FE, LE, and OE scores by the total number of errors (FE + LE + OE) for that visual field. Normalized error scores were subjected to an analysis of variance with visual field condition and error type as within-subjects variables. Figure 2 shows the normalized percentage of errors of each type for each visual field for Experiment 1. There was a significant main effect of error type, with more normalized LEs than OEs and more normalized OEs than FEs, F(2,38)=27.22, MSE = .0626, p < .001. There was also a significant Error Type by Visual Field interaction, F(4,76)=5.836, MSE = .0324, p < .001. This interaction defines a qualitative difference in performance (Hellige, 1983) and indicates that patterns of performance vary across the visual field presentation conditions. As Figure 2 indicates, the LVF/right hemisphere condition showed significantly fewer FEs than the other two conditions. However, the RVF/left hemisphere condition showed Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 14 60 5 0 - (0 o k_ 4 0 - UJ o a > O ) a c a > o o a. ■ o 8 3 0 - 2 0 - (B E >_ o z LVF RVF BILATERAL 1 0 - CE F E LE Error Type Figure 2. Percentage of errors for each of the three visual field conditions in Experiment 1. Error bars show standard errors computed from the within-subject error term (Loftus & Masson, 1994). (FE = normalized first-letter errors; LE = normalized last-Ietter errors; OE = normalized other errors.) significantly fewer LEs than the other two conditions. In order to examine this interaction, analyses were conducted comparing LVF/right hemisphere trials with RVF/left hemisphere trials, LVF/right hemisphere with BILATERAL trials; and RVF/left hemisphere with BILATERAL trials. Both the LVF/right hemisphere vs. RVF/left hemisphere and the RVF/left hemisphere vs. BILATERAL analyses showed significant Error Type by Visual Field interactions, £ < .01. However, the LVF/right Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 15 hemisphere vs. BILATERAL analysis did not show a significant Error Type by Visual Reid interaction, p =. 118. The lack of a significant interaction suggests that BILATERAL performance is similar to LVF/right hemisphere performance. To simplify the comparison of error patterns across the three visual field conditions, we calculated a qualitative error score (QE) for each condition using the following formula: (LE - FE) / (FE + OE + LE), which normalizes overall error rates. This QE score is larger when proportionately more LEs than FEs occur and thus can be taken as a measure of how attention has been distributed across the three letters of the CVC. A lower QE score would suggest more holistic processing, while a higher QE score would suggest more sequential processing. This calculation yielded QE scores of .4611,. 1950, and .3531 for the LVF/right hemisphere, RVF/left hemisphere, and BILATERAL conditions respectively. Subtracting the QE score for the RVF/left hemisphere from the QE score for the LVF/right hemisphere yields a left- right asymmetry measure of .2661, which again is similar to that reported in previous experiments (Hellige et al., 1989, Experiment 2: .3120; Eng & Hellige, 1994, Experiment 2 CVCs: .2500; Luh & Levy, 1995: .3810). The QE scores were subjected to an analysis of variance with visual field as the within-subjects variable. There was a significant main effect of visual field, F(2,38) = 8.39, MSE = .0427, pc.001. Subsequent pairwise comparisons showed that the BILATERAL QE score was not significantly different from the LVF/right hemisphere QE score, p = . 11. All other pairs differed significantly, p<.05 The pattern of errors on BILATERAL trials and the QE scores for BILATERAL trials have always been found to be intermediate between the results for unilateral trials in CVC recognition experiments. Hellige and his colleagues have found BILATERAL performance to be statistically equivalent to LVF/right hemisphere Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 16 performance on these dimensions (Eng & Hellige, 1994; Hellige et al., 1989, Hellige et al., 1994). However, Luh and Levy and their colleagues (Luh, 1993; Luh & Levy, 1995) have found BILATERAL performance to be different from both LVF/right hemisphere and RVF/left hemisphere performance. It is unclear why these differing results have been found, given that the stimuli and procedures are much the same. The analysis of total error rates for Experiment 1 supports the hypothesis that both hemispheres are contributing to performance on BILATERAL trials, each in its characteristic mode, as suggested by Luh and Levy (1995). The expectation then would be that BILATERAL patterns of performance should represent an average of left hemisphere and right hemisphere performance. Even though BILATERAL error patterns did not differ significantly from LVF error patterns, it is still possible that they also did not differ from the average of LVF and RVF patterns. Therefore, an additional test for an Error Type by Visual Field interaction was performed, comparing BILATERAL trials with the average of the two unilateral trial types. This interaction was significant, p = .03. Although the error pattern on BILATERAL trials was intermediate between those found on LVF/right hemisphere and RVF/left hemisphere trials, it is apparently not an average of the two. On the other hand, a comparison of the BILATERAL QE score with the average of the unilateral QE scores showed no significant difference, p = .69. It may be that the error pattern on BILATERAL trials was distorted because performance was so high. There were practically no failures to identify all three of the three letters on BILATERAL trials, although this type of OE represented about 10% of the normalized proportion of errors for unilateral trials. Given this consideration and the statistical equivalence of BILATERAL QE scores with the average of unilateral QE scores, the results of Experiment 1 are not Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 17 inconsistent with a model of interhemispheric cooperation in which both hemispheres contribute to performance when identical stimulus information is presented bilaterally. The fact that the quantitative results for BILATERAL trials are predicted by the binomial theorem when noise stimuli are used, but not when the visual field contralateral to the CVC is empty on unilateral trials, suggests that the two cerebral hemispheres share some pool of common processing resources. When noise stimuli are not used on unilateral trials, the hemisphere to which the CVC is directed is able to draw on this pool with no competition from the unstimulated hemisphere. However, on BILATERAL trials, the two hemispheres must divide the available processing resources, so that each one has fewer resources to devote to processing its CVC than it has on unilateral trials. When noise stimuli are used to equate attentional demands over the various trial types, the binomial theorem allows an accurate prediction of BILATERAL performance from performance on RVF/left hemisphere trials and LVF/right hemisphere trials. Experiment 2 In Experiment 1, the number of physical stimuli present and the number of hemispheres stimulated were equated for the three trial types; however, there were two copies of the target presented on BILATERAL trials, but only one copy of the target on target-unilateral trials. Additionally, there was a noise stimulus present on target- unilateral trials, but no noise stimulus on BILATERAL trials. Performance on BILATERAL trials demonstrated a clear redundancy gain in line with the predictions of the binomial theorem, but it remains unclear how much of the overall quantitative performance advantage on BILATERAL trials was due to having two copies of the target available for processing (rather than one, as in unilateral trials) and how much might be due to the advantage of cooperative bihemispheric processing. To sort out Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 18 these possible contributions, in Experiment 2 both the number of physical stimuli and the number of copies of the target were held constant: two copies of the target and two copies of the noise stimulus were presented on each trial. Since two copies of the target were presented on all trials, no redundancy gain was expected for the bilateral as compared to the unilateral conditions. However, if there is an advantage to having both hemispheres participate in the identification task, then performance on bilateral trials should be significantly better than the average of performance on unilateral trials (Liederman, 1986). Method Participants. Twelve men and 12 women from the same population described for Experiment 1 served as participants in Experiment 2. Their ages ranged from 17 to 33 years (M = 20.0 (S.D. = 3.46) Apparatus, stimulus materials, and procedure. Experiment 2 was identical in all respects to Experiment 1 except that stimuli were presented in four positions on the screen, and each participant completed two sets of three blocks of trials. There were two LVF positions, both 3° left of center, one above the other. The upper position was centered at 2.4° above the meridian, and the lower position was centered at 2.4° below the meridian. The interval between the bottom of the upper trigram and the top of the lower trigram was 1.6°. The two RVF positions were similarly located on the right. In the left-visual-field-targets condition (LVF/right hemisphere), the CVC was presented in the LVF upper position and the LVF lower position. In the right-visual-field-targets (RVF/left hemisphere) condition, the CVC was presented in the RVF upper position and the RVF lower position. The four target-bilateral ( BILATERAL) arrangements were; 1) Diagonal UP: the CVC was presented diagonally in the LVF lower position and the RVF upper position; 2) Diagonal DOWN: the CVC was presented diagonally Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 19 in the LVF upper position and the RVF lower position; 3) TOP: the CVC was presented in the LVF upper position and the RVF upper position; and 4) BOTTOM: the CVC was presented in the LVF lower position and the RVF lower position. In each condition, the positions not occupied by CVCs contained foils. Thus, in all six conditions, two copies of the CVC and two copies of the foil were presented. Illustrations of these three viewing conditions are given in Figure 3. The diagonal (UP and DOWN) trials were selected as the best control conditions for the target-unilateral conditions, because in these diagonal arrangements one copy of the target was above the horizontal meridian and one was below, just as in the LVF/right hemisphere and RVF/left hemisphere conditions. The only difference between diagonal trials, on the one hand, and LVF/right hemisphere and RVF/left hemisphere trials, on the other hand, was that in the diagonal trials, one copy of the target was presented initially to each hemisphere, while in the unilateral trials, both copies of the target were presented to the same hemisphere. This crossed-field vs. uncrossed-field presentation is the crucial difference for Experiment 2, so the diagonal trials were felt to constitute the best contrast to the unilateral trials. In addition, the diagonal placement of stimuli may serve to reduce any scanning effects related to reading (Banich & Karol, 1992; Bryden, 1961; Heron, 1957). TOP and BOTTOM trials were included to discourage the development of a strategy of scanning top to bottom on all trials. In reporting the results of Experiment 2, all references to BILATERAL trials are to the average of the UP and DOWN trials, since these trial types were found to be statistically equivalent to each other in preliminary analyses. All BILATERAL trials were assigned to one of the four target-bilateral arrangements. Four versions of the stimulus files were prepared in order to counterbalance this assignment, with each CVC appearing in one of the four possible Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 20 z' X D X A X G + X D X A X G \ ) Uni 1 at er al RVF/ LH f \ D X A X G X + X D X A X G V J r \ D X A X G X + D X A X G X J Uni later al LVF/ RH X D X A X G + D X A X G X ) Bilateral UP Bilateral DOWN \ X X X X X X + D D A A G G \ ______________________ y Bilateral BOTTOM Figure 3. Illustrations of the same CVC targets presented in different viewing conditions in Experiment 2. BILATERAL arrangements in each version. However, preliminary analyses showed no effect of this manipulation, so the results presented in this paper are collapsed across stimulus file version. Immediately upon completion of the first experimental set, consisting of 3 blocks of 37 trials, participants began a second set. The exposure duration for the last Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Bilateral TO3 21 trial of the first set was used to determine the exposure duration for the first trial of the second set. Two sets were used to insure a sufficient number of trials of each of the target-bilateral arrangements for analysis. Preliminary analyses showed no effect of set (except for shorter mean exposure times on the second set), so the results presented in this paper are collapsed across experimental sets. Results and Discussion The titration of exposure durations again resulted in approximately equal durations for all visual field conditions: LVF, M = 112 ms; RVF, M = 110 ms; BILATERAL, M = 109 ms. Exposure times were substantially longer than in Experiment 1, reflecting the greater processing demands from having four stimuli (two copies of the target syllable and two copies of the foil) displayed on each trial. The titration of exposure durations was successful in achieving a total error rate near 50% (specifically 47.9%, S.D. = 3.7%). The error rates for the three visual field conditions differed significantly, F(2,46) = 21.79, MSE = .0101, gc.OOl. The error rate for the LVF/right hemisphere (58.0%, S.D. = 8.6%) was larger than that for the RVF/left hemisphere (39.8%, S.D. = 10.0%), showing a left hemisphere advantage of 18.2%, which is quite similar to the 20% advantage found in Experiment 1. Subsequent post hoc comparisons showed that the LVF/right hemisphere differed from the RVF/left hemisphere and the BILATERAL (44.1%, S.D. = 8.5%) significantly in error rate (g < .001 in both cases). However, the error rates for the RVF/left hemisphere and the BILATERAL trials did not differ significantly (g = .14). Recall that in Experiment 1, performance in the BILATERAL condition reflected a significant redundancy gain. In Experiment 2, performance actually trended to be somewhat worse in the BILATERAL condition than in the better of the two unilateral conditions, although the difference was not statistically significant. This result was not unexpected: two copies Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 22 of the target were presented in all three visual conditions, so no redundancy gain would be predicted. However, an advantage might still be expected from having two processing units when the two copies of the stimulus were presented initially to different hemispheres. Some previous research has found an advantage for crossed- field conditions when stimuli to be compared were presented simultaneously (e.g., Davis & Schmit, 1971; Dimond & Beaumont, 1972; Hellige, 1987) and when the task was complex (Banich & Belger, 1990; Belger & Banich, 1992). To test for an advantage of bihemispheric cooperation in the present experiment, the BILATERAL error rate (44.1%) was compared with the average of the two unilateral error rates (48.9%) and was found to be significantly lower (g < .05). This result is consistent with the interpretation that although there is no redundancy gain when equal numbers of targets are presented in all conditions, there is still an advantage of bihemispheric processing. Error patterns were analyzed as in Experiment 1, with all errors for each visual field classified as FE (first-letter errors), LE (last-letter errors) or OE (other errors) and then normalized by dividing by the total number of errors for that visual field. Normalized error scores were subjected to an analysis of variance with visual field condition and error type as within-subjects variables. Figure 4 shows the normalized percentage of errors of each type for each visual field for Experiment 2. There was a significant main effect of error type, with more normalized LEs than OEs and more normalized OEs than FEs, F(2,46) = 56.89, MSE = .0444, g < .001. There was also a significant Error Type by Visual Field interaction, F(4,92) = 5.70, MSE = .0169, g < .001. As Figure 4 indicates, the RVF/left hemisphere showed significantly more FEs than the other two conditions and significantly fewer LEs than the LVF/right Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 23 60 c o k . 2 o © 8 ) < 0 c © u k_ © CL $ N 2 0 - « E o z LVF RVF BVF CE F E LE Error Type Figure 4. Percentage of errors for each of the three visual field conditions in Experiment 2. Error bars show standard errors computed from the within-subject error term (Loftus & Masson, 1994). (FE = normalized first-letter errors; LE = normalized last-letter errors; OE = normalized other errors.) hemisphere (p < .001). The RVF/left hemisphere also trended to show fewer LEs than the BILATERAL, just missing conventional statistical significance at p = .051. In order to examine this interaction, analyses were conducted comparing LVF/right hemisphere trials with RVF/left hemisphere trials, LVF/right hemisphere with BILATERAL trials; and RVF/left hemisphere with BILATERAL trials. Both the LVF/right hemisphere vs. RVF/left hemisphere and the RVF/left hemisphere vs. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 24 BILATERAL analyses showed significant Error Type by Visual Field interactions, F(2,46) = 8.37, M SE= .0198, p < .001; F(2,46) = 4.73, MSE = .0168, p < .05. The LVF/right hemisphere vs. BILATERAL analysis just missed conventional levels of significance in showing a significant Error Type by Visual Field interaction, F(2,46) = 3.085, MSE = .0140, p = .055. Thus it appears that the distribution of errors is different in all three visual field conditions, although the BILATERAL error pattern may be somewhat more similar to the LVF/right hemisphere pattern than to the RVF/left hemisphere pattern. To further investigate the pattern of normalized errors across visual fields, qualitative error scores were calculated. Recall that the QE score is the difference between the normalized proportion of LEs and FEs and thus serves as an index of how sequential processing is. This calculation yielded QE scores of .4583, .2326, and .3916 for the LVF/right hemisphere, RVF/left hemisphere, and BILATERAL conditions respectively. Subtracting the QE score for the RVF/left hemisphere from the QE score for the LVF/right hemisphere yields a left-right asymmetry measure of .2257, which is somewhat lower than has been found previously. An ANOVA with visual field as the within-subjects variable showed a significant main effect of visual field, F(2,46) = 13.15, M SE= .0245, p < . 001. Subsequent pairwise comparisons showed that the RVF/left hemisphere QE differed significantly from both the LVF/right hemisphere QE score and the BILATERAL QE score, p < .001. However, the LVF/right hemisphere QE score did not differ significantly from the BILATERAL QE score, p = .147. The inference again is that BILATERAL processing was more similar to LVF/right hemisphere processing than to RVF/left hemisphere processing. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 25 General Discussion The present experiments were designed to investigate performance in the lateralized syllable identification task when number of physical stimuli and number of copies of the target stimulus were held constant across visual field presentation conditions. In the CVC experiments previously reported in which a bilateral condition was used to investigate performance when both hemispheres received identical stimulus information, two copies of the target stimulus were presented on bilateral trials, but only one copy of the target stimulus was presented on unilateral trials and only one hemisphere was stimulated. The contralateral field was left blank. Under these conditions, a substantial redundancy gain might be expected for the bilateral trials, but it has not been found. Instead, performance on bilateral trials has been sometimes only marginally better than in the better of the two unilateral conditions and sometimes statistically equivalent and even trending to be worse, as discussed earlier. From these results and the pattern of qualitative performance, Hellige et al. (1989) argued that the two hemispheres were not contributing equally and independently to the processing of bilateral redundant stimuli, each using its preferred mode of processing, but that instead both hemispheres were operating in a relatively inefficient serial manner. Luh and Levy (1995) offered evidence that both hemispheres were contributing to the pattern of bilateral performance. They suggested that although there is an advantage to having both hemispheres working together to process bilateral stimuli, this advantage is offset by the attentional costs of dividing processing between the two visual fields. The results of the present Experiment 1 demonstrate that when attentional resources are controlled (by adding a noise stimulus to the contralateral visual field), the redundancy gain predicted by the binomial theorem does emerge for Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 26 target-bilateral trials. Performance in the bilateral redundant condition is substantially better than performance in the better of the two unilateral conditions. It appears that in the standard CVC paradigm, the redundant-targets advantage is indeed offset by an attentional cost of having two stimuli competing for the attentional resources. Such a cost of even redundant targets has been previously reported (Grice et al., 1984; Hellige et al., 1988). In the current experiments, it appears that this cost is due to the division of a unitary processing resource shared by the two hemispheres, such that each copy of the stimulus is less fully processed than if it were the only stimulus presented. In Experiment 1, a performance advantage in the target-bilateral condition could emerge because of a redundant targets effect or because of some advantage of splitting the inputs between the two hemispheres. To disambiguate these two potential sources of performance advantages and to study the issue of a possible advantage from interhemispheric cooperation, it is necessary to equate the number of copies of the target stimulus presented in each visual field condition. In Experiment 1, two copies of the target stimulus were presented in the bilateral condition, but only one copy of the target stimulus was presented in the unilateral conditions. Therefore the performance advantage on bilateral trials could be attributed entirely to a redundant targets effect. In Experiment 2 the number of copies of the target was held constant, and the critical difference between target-unilateral trials and target-bilateral trials was whether or not initial processing was divided between the two cerebral hemispheres. The appropriate comparison to test for the presence of an interhemispheric cooperation effect is of the target-bilateral condition with the average of the target-unilateral conditions (Liederman, 1986). This comparison yielded a small but statistically significant advantage for the target-bilateral condition in Experiment 2. This advantage may indicate that each hemisphere has some individual processing resources, unshared by Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 27 the other hemisphere, that can be tapped when input is bihemispheric (cf. Hellige & Wong, 1983; Herdman & Friedman, 1985). However, the evidence is only suggestive, since the two stimuli in a single visual field on unilateral trials may not contribute equally to performance, so the average of unilateral performance might somewhat underestimate bilateral performance. It is difficult to estimate what the individual contributions of the two hemispheres are when only one target is presented to each hemisphere, and this difficulty represents a limitation of the present experiments. The finding of a substantial redundancy gain for bilateral redundant presentation in Experiment 1 relative to target-unilateral presentation implies that both hemispheres contribute substantially to performance when identical stimulus information is presented in the two visual fields. In order to achieve the degree of accuracy predicted by the binomial formula, the two hemispheres must not only work individually to achieve a percept of the target syllable, but they must also cooperate to select a correct response. When both hemispheres identify the syllable correctly, it is clear that a correct response will be given. This state of affairs is represented in the binomial formula by the intersection term: P(LVF)*P(RVF). When neither hemisphere is able to identify the target syllable correctly, it is clear that an incorrect response will be given. In the case that one hemisphere has achieved a correct percept and the other is in error, the situation is less straightforward. The assumption of the binomial formula is that subjects always or nearly always choose the correct response when the two hemispheres are in conflict. Levy et al. (1983) suggest that metalinguistic processes, usually lateralized in the left hemisphere, are responsible for d is c rim in atin g correct from incorrect performance. Subjects in their study indicated a confidence rating in addition to syllable identification. They were able, well above chance, to Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 28 discriminate their correct from their incorrect performance. Further evidence that the brain is able to monitor its own performance on syllable identification and respond appropriately is offered by analysis of the effects of correctness or incorrectness of previous trials on performance on current trials. Levy, Wagner, and Luh (1990) reported that when an error was made on a previous trial, performance on the subsequent trial improved significantly. This effect was strongest for RVF trials when the previous trial was an RVF trial to which an incorrect response had been given. Thus it seems reasonable to suppose that the brain is able to discriminate clear, accurate percepts from less clear, inaccurate ones. To the extent that this discrimination process is imperfect, we would expect to see bilateral performance below the level predicted by the binomial theorem. Since the results of Experiment 1 show bilateral performance equaling the predicted level, we may surmise either that the discrimination of correct responses is highly accurate or that additional factors were at work to improve performance, perhaps including some advantage of dividing initial processing between the two hemispheres, or both. The results of the qualitative analysis of error patterns in the present experiments are suggestive, but questions remain. It is unclear why bilateral presentations should lead to a more sequential mode of processing of CVCs, similar to that seen for LVF/right hemisphere presentations, considering that this sequential strategy is less efficient than the more holistic strategy of the left hemisphere. One possible problem in interpreting the results of CVC studies in terms of their implications for modes of interhemispheric communication and cooperation is that since overall levels of performance differ for LVF, RVF, and bilateral presentations, it has been necessary to apply statistical normalization procedures in order to make fair qualitative comparisons. One might inquire how performance patterns might differ if Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 29 the level of accuracy was held constant across conditions using experimental controls rather than statistical correction. This would be possible through separate titration of exposure durations for the LVF, RVF, and bilateral stimuli. An interesting theoretical question raised by the present experiments is the locus of redundant targets and interhemispheric cooperation effects. Since redundant CVC stimuli were always physically identical, it is not possible to disentangle perceptual from semantic effects. Information might be shared between the hemispheres at a relatively low perceptual level or at a later semantic level. One way to differentiate these possibilities would be to introduce a case and font manipulation into the current Experiment 1 paradigm, such that bilateral redundant targets are sometimes in the same case and font and sometimes in a different case and font. If low level perceptual effects account for a significant portion of the performance advantage on bilateral trials, then varying the case and font of the two targets will attenuate these effects, but if semantic information is shared, then the bilateral performance advantage should remain when case and font are varied. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 30 References Banich, M. T., & Belger, A. (1990). Interhemispheric interaction: How do the hemispheres divide and conquer a task? Cortex. 26. 77-94. Banich, M. T., & Karol, D. L. (1992). The sum of the parts does not equal the whole: evidence from bihemispheric processing. Journal of Experimental Psychology: Human Perception and Performance. 18. 763-784. Belger, A., & Banich, M. T. (1992). Interhemispheric interaction affected by computational complexity. Neuropsvchologia. 30. 923-929. Boles, D. B. (1983). Hemispheric interaction in visual field asymmetry. Cortex. 19. 99-113. Boles, D. B. (1990). What bilateral displays do. Brain and Cognition. 12. 205-228. Boles, D. B. (1995). Parameters of the Bilateral Effect. In F. L. Kitterle (Ed.), Hemispheric communication: Mechanisms and models (pp. 211-230). Hillsdale, NJ: Erlbaum. Bryden, M. P. (1961). The role of post-exposural eye movements in tachistoscopic presentation. Canadian Journal of Psychology. 15. 220-225. Bryden, M. P. & Bulman-Fleming, M. B. (1994). Laterality effects in normal subjects: Evidence for interhemispheric interactions. Workshop on the Corpus Callosum and Interhemispheric Transfer (1992, Priorij Corsendonk, Belgium). Behavioural Brain Research. 64. 119-129. Butler, K., & Bryden, M. P. (1990). Hemispheric asymmetries in the identification of faces and emotional expressions. Journal of Clinical and Experimental Neuropsychology. 12, 38. Cherry, B. J., Hellige, J. B., & McDowd, J. M. (1995). Age differences and similarities in patterns of cerebral hemispheric asymmetry. Psychology and Aging. 10. 191-203. Davis, R., & Schmit, V. (1971). Timing of the transfer of information between the hemispheres in man. Acta Psvchologica. 35. 335-346. Dimond, S. J., & Beaumont, G. (1972). Processing in perceptual integration between and within the cerebral hemispheres. British Journal of Psychology. 63. 509- 514. Duncan, J. (1980). The locus of interference in the perception of simultaneous stimuli. Psychological Review. 87. 272-300. Eng, T. L., & Hellige, J. B. (1994). Hemispheric asymmetry for processing unpronounceable and pronounceable letter trigrams. Brain and Language. 46. 517-535. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 31 Grice, G. R., Canham, L., & Gwynne, J. W. (1984). Absence of a redundant-signals effect in a reaction time task with divided attention. Perception & Psvchophvsics. 36. 565-570. Hellige, J. B. (1983). Hemisphere by task interaction and the study of laterality. In J. B. Hellige (Ed.), Cerebral hemisphere asymmetry: Method, theory and application (pp. 411-443) New York: Praeger. Hellige, J. B. (1987). Interhemispheric interaction: Models, paradigms, and recent findings. In D. Ottoson (Ed.), Duality and unitv of the brain (pp. 454-465). New York: Plenum Press. Hellige, J. B., Bloch, M. I., Cowin, E. L., Eng, T. L., Eviatar, Z., & Sergent, V. (1994). Individual variation in hemispheric asymmetry: Multitask study of effects related to handedness and sex. Journal of Experimental Psychology: General. 123. 235-256. Hellige, J. B., & Cowin, E. L. (1996). Effects of stimulus arrangement on hemispheric differences and interhemispheric interaction for processing letter trigrams. Neuropsychology. 10. 247-253.' Hellige, J. B., Cowin, E. L., & Eng, T. L. (1995). Recognition of CVC syllables from LVF, RVF, and central locations: Hemispheric differences and interhemispheric interaction. Journal of Cognitive Neuroscience. 7. 258-266. Hellige, J. B., Jonsson, J. E., & Michimata, C. (1988). Processing from LVF, RVF, and BILATERAL presentations: Examinations of metacontrol and interhemispheric interaction. Brain and Cognition. 7. 39-53. Hellige, J. B., Taylor, A. K., & Eng, T. L. (1989). Interhemispheric interactions when both hemispheres have access to the same stimulus information. Journal of Experimental Psychology: Human Perception and Performance. 1.711- 722. Hellige, J. B., & Wong, T. M. (1983). Hemisphere-specific interference in dichotic listening: Task variables and individual differences. Journal of Experimental Psychology: General. 112. 218-239. Herdman, C., & Friedman, A. (1985). Multiple resources in divided attention: A cross-modal test of the independence of hemispheric resources. Journal of Experimental Psychology: Human Perception and Performance. 11.40-49. Heron, W. (1957). Perception as a function of retinal locus and attention. American Journal of Psychology. 70. 39-48. Hines, D. (1975). Independent functioning of the two cerebral hemispheres for recognizing bilaterally presented visual-half-field stimuli. Cortex. 11. 132-143. Jones, B. (1982). The integrative action of the cerebral hemispheres. Perception & Psvchophvsics. 32. 423-433. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 32 Levy, J., Heller, W., Banich, M. T., & Burton, L. A. (1983). Are variations among right-handed individuals in perceptual asymmetries caused by characteristic arousal differences between hemispheres? Journal of Experimental Psychology: Human Perception and Performance. 9. 329-359. Levy, J., & Reid, M. (1978). Variations in cerebral organization as a function of handedness, hand posture in writing, and sex. Journal of Experimental Psychology: General. 107. 119-144. Levy, J., Wagner, N., & Luh, K. (1990). The previous visual field: Effects of lateralization and response accuracy on current performance. Neuropsvchologia. 28. 1239-1249. Liederman, J. (1986). Determinants of the enhancement of the right visual field advantage by bilateral vs. unilateral stimuli. Cortex. 22. 553-565. Liederman, J., Merola, J., & Martinez, S. (1985). Interhemispheric collaboration in response to simultaneous bilateral input. Neuropsvchologia. 23. 673-683. Loftus, G. R., & Masson, M. E. J. (1994). Using confidence intervals in within- subject designs. Psvchonomic Bulletin & Review. 1. 476-490. Ludwig T. E., Jeeves, M. A.; Norman, W. D.; & DeWitt, R. (1993). The bilateral field advantage on a letter-matching task. Cortex. 29. 691-713. Luh, K. E. (1993). Interhemispheric transfer of bilateral linguistic stimuli. Society for Neuroscience Abstracts. 19. 1808. Luh, K. E., & Levy, J. (1995). Interhemispheric cooperation: Left is left and right is right, but sometimes the twain shall meet. Journal of Experimental Psychology: Human Perception and Performance. 21. 1243-1258. McKeever, W. F. (1971). Lateral word recognition: Effects of unilateral and bilateral presentation, asynchrony of bilateral presentation, and forced order of report. Quarterly Journal of Experimental Psychology. 23. 410-416. McKeever, W. F., & Huling, M. (1971). Lateral dominance in tachistoscopic word recognition performance obtained with simultaneous bilateral input. Neuropsvchologia. 9. 15-20. Merola, J., & Liederman, J. (1990). The extent to which between-hemisphere division of inputs improves performance depends upon task difficulty. Journal of Clinical and Experimental Neuropsychology. 10. 69. Norman, W. D., Jeeves, M. A., Milne, A., & Ludwig, T. (1992). Hemispheric interactions: The bilateral advantage and task difficulty. Cortex. 28. 623-642. Oldfield, R. C. (1971). The assessment of handedness: The Edinburgh inventory. Neuropsvchologia. 9. 97-111. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 33 Young, A. W., & Bion, P. J. (1981). Accuracy of naming laterally presented known faces by children and adults. Cortex. 17. 97-106. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. IMAGE EVALUATION TEST TARGET (Q A -3 ) y I <v / , 150mm IIW 1 G E . In c 1653 E ast Main Street R ochester. NY 14609 USA Phone: 716/482-0300 Fax: 716/288-5989 C 1993. Applied Image. Inc. A ll Rights Reserved Reproduced with permission of the copyright owner. Further reproduction prohibited without permission.
Linked assets
University of Southern California Dissertations and Theses
Conceptually similar
PDF
Interhemispheric interaction in bilateral redundancy gain: Effects of physical similarity
PDF
Effects of personal resource sufficiency on perceived difficulty and desirability of earthquake preparedness
PDF
Hedonic aspects of conditioned taste aversion in rats and humans
PDF
Aging and the use of context and frequency information in ambiguity resolution
PDF
Head injury and dementia: A co-twin control study of Swedish twins
PDF
Effects of threat and self-focus on consensual bias in majorities
PDF
Content analysis of articulated thoughts of chronic worriers
PDF
Explanations, the availability heuristic, and biases of subjective likelihood in economics
PDF
Applying the theory of reasoned action to condom use: The effect of immediate consequences on intention-behavior consistency
PDF
An examination of invariance using cognitive training data of older adults
PDF
Asymmetries in the bidirectional associative strengths between events in cue competition for causes and effects
PDF
Invariance to changes in contrast polarity in object and face recognition
PDF
Alcohol treatment entry and refusal in a sample of older veterans
PDF
Adolescents' social attitudes: Genes and culture?
PDF
Intragroup evaluations, attitude source, and in-group member derogation
PDF
Hyperactive symptoms, cognitive functioning, and drinking habits
PDF
Effects of a corneal anesthetic on the extinction of the classically conditioned response in the rabbit
PDF
Adaptation to sine-wave gratings selectively reduces the sensory gain of the adapted stimuli
PDF
Depression and suicidality in Latino adolescents: A study of acculturation and gender role beliefs
PDF
A medley of metaphors
Asset Metadata
Creator
Marks, Nancy Lee
(author)
Core Title
Effects of bilateral stimulation and stimulus redundancy on performance in processing nonword letter trigrams
School
Graduate School
Degree
Master of Arts
Degree Program
Psychology
Publisher
University of Southern California
(original),
University of Southern California. Libraries
(digital)
Tag
OAI-PMH Harvest,psychology, cognitive
Language
English
Contributor
Digitized by ProQuest
(provenance)
Advisor
[illegible] (
committee chair
), Lavond, David (
committee member
), Walsh, David A. (
committee member
)
Permanent Link (DOI)
https://doi.org/10.25549/usctheses-c16-25387
Unique identifier
UC11337402
Identifier
1393178.pdf (filename),usctheses-c16-25387 (legacy record id)
Legacy Identifier
1393178.pdf
Dmrecord
25387
Document Type
Thesis
Rights
Marks, Nancy Lee
Type
texts
Source
University of Southern California
(contributing entity),
University of Southern California Dissertations and Theses
(collection)
Access Conditions
The author retains rights to his/her dissertation, thesis or other graduate work according to U.S. copyright law. Electronic access is being provided by the USC Libraries in agreement with the au...
Repository Name
University of Southern California Digital Library
Repository Location
USC Digital Library, University of Southern California, University Park Campus, Los Angeles, California 90089, USA
Tags
psychology, cognitive